This invention relates generally to the fabrication of microelectronic devices, and more particularly to cleaning a contact hole after etching.
Microelectronic device fabrication entails subjecting a substrate to various combinations of layering, patterning, doping, and heat treating processes to form electronic devices in and on the substrate. Out of the four categories of processes, the patterning process plays an especially important role in setting the critical dimension (CD) of the electronic devices. The patterning process entails removing selected portions of surface layers on a substrate. Thus, errors in the patterning process can cause distorted or misplaced patterns, which may in turn cause defects in the electrical functioning of the device or circuit. Likewise, contamination during the patterning process can introduce defects in the device and circuit.
During the patterning process, selected portions of a surface may be removed to form a contact hole. Different types of etching, such as conventional wet etching or dry etching, are commonly used to form the contact hole. Dry etching methods, such as a conventional plasma etching method, are typically preferred for semiconductor devices that require small CDs because they tend to result in more precise etching than conventional wet etching methods.
The etching process tends to leave photoresist residues, etch byproducts, and damaged silicon at the bottom of the contact hole. As some of the residues and byproducts are insulative, their presence in the contact hole can degrade the quality of electrical contact between circuit components and ultimately lead to device defects. One of the methods for removing the residues, byproducts, and damaged silicon inside a contact hole involves utilizing plasma (e.g., radio frequency (RF)xe2x80x94plasma, microwave plasma, or inductively coupled plasma) that includes fluorine. Fluorine is an etchant for the residues, byproducts, and damaged silicon. Unfortunately, exposing the contact hole to fluorine-containing plasma has an undesirable side effect of laterally etching the contact hole sidewall, thereby changing the CD and the shape of the contact hole. This side effect is experienced with many common sidewall materials such as spin-on-glass (SOG) and hydrogen silsesquioxane (HSQ), and is especially pronounced with doped silicon dioxide such as phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), borosilicate glass (BSG), and borophospho tetraethyl orthosilicate (BPTEOS), the lattice structure of which is already disrupted by doping. This lateral etching side effect makes typical fluorine-plasma cleaning methods less than suitable for devices that are sensitive to changes in the critical dimension, such as devices having feature sizes below 0.25 microns. As feature sizes of electronic devices become smaller, the electronic devices become more sensitive to errors and contamination. Thus, as the feature sizes of electronic devices become smaller, there is a growing need for a method of cleaning a contact hole without lateral etching.
The present invention allows removal of etch byproducts, residues, and damaged silicon inside a contact hole while minimizing lateral etching of the contact hole. The byproducts, residues, and damaged silicon are herein collectively referred to as xe2x80x9cbyproducts.xe2x80x9d The byproducts are removed through a chemical reaction wherein the reactive gases, such as fluorine in the form of RF plasma, are put in contact with the byproducts. During this reactive cleaning process, the reactants also come in contact with the sidewall of the contact hole and react with the sidewall material. Adding hydrogen gas to the RF plasma in accordance with the present invention allows the reactants to remove the byproducts and residues without laterally etching the contact hole sidewall. By minimizing lateral etching of the contact hole sidewall, the hydrogen gas reduces any changes to the shape and dimensions of the contact hole.
After an etching process, a wafer is mounted on a platen inside an RF plasma reaction chamber. The platen is coupled to an RF source. The reaction chamber is adjusted to an appropriate pressure (e.g., about 250-1000 mTorr), and a gas mixture is introduced into the chamber. The gas mixture may include approximately 10-60% hydrogen gas, a gas (e.g., NF3) that removes the byproducts and residues, and nitrogen gas. The cleaning reaction is compatible with most conventional dry etching or a wet etching processes. The present invention may be used for any microelectronic devices for which maintenance of critical dimension plays an important role in preventing defects. The present invention is especially useful for devices having feature sizes less than 0.25 xcexcm.